Method and apparatus for accurate die-to-wafer bonding

ABSTRACT

A method of light-emitting diode (LED) packaging includes coupling a number of LED dies to corresponding bonding pads on a sub-mount. A mold apparatus having concave recesses housing LED dies is placed over the sub-mount. The sub-mount, the LED dies, and the mold apparatus are heated in a thermal reflow process to bond the LED dies to the bonding pads. Each recess substantially restricts shifting of the LED die with respect to the bonding pad during the heating.

BACKGROUND

Light-emitting diode (LED) devices has experienced rapid growth inrecent years. LED devices emit light when a voltage is applied. LEDdevices have increasingly gained popularity due to favorablecharacteristics such as small device size, long lifetime, efficientenergy consumption, and good durability and reliability.

The fabrication of LED devices may involve a die-to-wafer bondingprocess, in which a plurality of LED dies are bonded to a plurality ofbonding pads on a wafer. Conventional die-to-wafer bonding processes useauto die-bonding machines with a flux reflow oven or eutecticdie-to-wafer bonders. During the bonding process, LED dies shift theirlateral positions with respect to the bonding pads in any givendirection. In some cases, the die-shift may exceed +/−38 microns. As theLED die size continues to decrease, the die-shift of conventional LEDbonding processes is becoming a bigger issue because the reduction ofreliability and performance for smaller LED devices is greater.

Therefore, although conventional LED die-to-wafer bonding processes havebeen generally adequate for their intended purposes, they have not beenentirely satisfactory in every aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIGS. 1-2 are diagrammatic fragmentary cross-sectional side views of aportion of a wafer having photonic devices disposed thereon at variousstages of fabrication in accordance with various aspects of the presentdisclosure.

FIG. 3 is a diagrammatic top view of a mold fixture.

FIG. 4 is a diagrammatic top view of a mold fixture and a wafer havingphotonic devices disposed thereon.

FIGS. 5-7 are diagrammatic fragmentary cross-sectional side views ofdifferent embodiments of a mold fixture being placed on a sub-mounthaving photonic devices disposed thereon.

FIG. 8 is a diagrammatic fragmentary cross-sectional side view of a moldfixture and a sub-mount having LED devices undergoing a bonding processin an oven.

FIG. 9 is a flowchart illustrating a method for fabricating a photonicdevice according to various aspects of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the formation of a first feature over or on a second feature in thedescription that follows may include embodiments in which the first andsecond features are formed in direct contact, and may also includeembodiments in which additional features may be formed interposing thefirst and second features, such that the first and second features maynot be in direct contact. Various features may be arbitrarily drawn indifferent scales for the sake of simplicity and clarity.

When turned on, light-emitting diode (LED) devices may emit radiationsuch as different colors of light in a visible spectrum, as well asradiation with ultraviolet or infrared wavelengths. Compared totraditional light sources (e.g., incandescent light bulbs), LED devicesoffer advantages such as smaller size, lower energy consumption, longerlifetime, variety of available colors, and greater durability andreliability. These advantages, as well as advancements in LEDfabrication technologies that have made LED devices cheaper and morerobust, have added to the growing popularity of LED devices in recentyears.

Nevertheless, existing LED fabrication technologies may face certainshortcomings. One such shortcoming is die shifting in a bonding process.In more detail, as part of a die-to-wafer bonding process of LEDdevices, a plurality of LED dies may be bonded to a plurality of bondingpads located on a wafer. Existing LED fabrication technologies mayutilize an auto die-bonding machine with flux reflow oven or eutecticdie-to-wafer bonders to carry out the die-to-wafer bonding process.However, these approaches used by the existing LED fabricationtechnologies allow some die shifting during the bonding. That is, whilethe LED dies are being bonded to the bonding pads, an LED die may shiftin a lateral direction with respect to the bonding pad below. In somecases, the amount of LED die shift may exceed +/−38 microns. As LED diesbecome smaller, such LED die shifting becomes increasingly undesirable,because it may lead to alignment challenges for later fabricationprocesses and may limit the applicability of advanced packagingprocesses.

According to various aspects of the present disclosure, described belowis an LED fabrication process that substantially overcomes the LED dieshifting issues present in existing LED fabrication processes. In moredetail, FIGS. 1 to 8 are diagrammatic fragmentary cross-sectional sideviews and top views of a portion of a wafer at various fabricationstages. Note that FIGS. 1 to 8 have been simplified to focus on theinventive concepts of the present disclosure.

Referring to FIG. 1, a sub-mount 30 is provided. The sub-mount 30 mayalso be referred to as a substrate or as a wafer. In one embodiment, thesub-mount 30 includes a semiconductor material, such as silicon (Si). Inother embodiments, the sub-mount 30 may include an aluminum nitride(AlN) material, an aluminum oxide (Al₂O₃) material, or a ceramicmaterial. Among other things, the sub-mount 30 may be used to provideelectrostatic discharge protection, efficient thermal dissipation (ofthe LED dies), and/or stress reduction. The sub-mount 30 is sufficientlythick, partly in order to ensure that the sub-mount 30 can perform thesefunctions adequately. In an embodiment, the sub-mount 30 has a thickness35 that is in a range from about 100 microns to about 400 microns. Inalternative embodiments, the thickness 35 may be thicker than 400microns.

A plurality of bonding pads are formed on the sub-mount 30. For the sakeof simplicity, only three of such bonding pads 40 are illustratedherein, but many more bonding pads are usually formed on the sub-mount30. The bonding pads 40 may also be referred to as a die-bonding padlayer. These bonding pads 40 are used for the bonding of photonicdevices such as LED dies in a bonding process. The bonding pads 40include a conductive material such as metal, which is both electricallyconductive and thermally conductive. In an embodiment, the bonding pads40 include gold (Au) and nickel (Ni). For example, the bonding pads 40may each include gold-plated nickel.

The bonding pads 40 each have a thickness 50. In an embodiment, thethickness 50 is in a range from about 1.5 microns to about 50 microns,for example, about 5 microns. The bonding pads 40 also each have alateral dimension 60. The lateral dimension 60 is measured horizontally(i.e., parallel to the surface of the sub-mount 30) in the figures shownherein. In an embodiment, the lateral dimension 60 is in a range fromabout 0.6 millimeters to about 6 millimeters, for example, about 1millimeter.

Next, a flux material 70 is provided on the bonding pads 40. The fluxmaterial 70 helps facilitate soldering by preventing oxidation andproviding chemical cleaning to the exposed surfaces of the bonding pads40. The flux material 70 may include water-soluble fluxes, no-cleanfluxes, or rosin fluxes. The flux material 70 on the bonding pads 40 isoptional and may be omitted in alternative embodiments.

Referring now to FIG. 2, a plurality of photonic devices are placed onthe bonding pads. For the sake of providing an example, three of suchphotonic devices 80 are shown in FIG. 2, though many more photonicdevices similar to the photonic devices 80 may be placed on the bondingpads. Each of the photonic devices 80 is placed on a respective one ofthe bonding pads 40.

In an embodiment, the photonic devices 80 include LED dies or LED chipsand may therefore be referred to as LED dies or LED devices 80thereafter. The LED devices 80 each include two oppositely dopedsemiconductor layers. In one embodiment, the oppositely dopedsemiconductor layers each contain a “III-V” family (or group) compound.In more detail, a III-V family compound contains an element from a “III”family of the periodic table, and another element from a “V” family ofthe periodic table. For example, the III family elements may includeBoron, Aluminum, Gallium, Iridium, and Titanium, and the V familyelements may include Nitrogen, Phosphorous, Arsenic, Antimony, andBismuth. In the present embodiment, the oppositely doped semiconductorlayers include a p-doped gallium nitride (GaN) material and an n-dopedgallium nitride material, respectively. The p-type dopant may includeMagnesium (Mg), and the n-type dopant may include Carbon (C) or Silicon(Si).

According to various embodiments, the LED devices 80 also each include amultiple-quantum well (MQW) layer that is disposed in between theoppositely doped layers. The MQW layer includes alternating (orperiodic) sub-layers of active material, such as gallium nitride andindium gallium nitride (InGaN). For example, the MQW layer may include anumber of gallium nitride sub-layers and a number of indium galliumnitride sub-layers, wherein the gallium nitride sub-layers and theindium gallium nitride sub-layers are formed in an alternating orperiodic manner. In one embodiment, the MQW layer includes tensub-layers of gallium nitride and ten sub-layers of indium galliumnitride, where an indium gallium nitride sub-layer is formed on agallium nitride sub-layer, and another gallium nitride sub-layer isformed on the indium gallium nitride sub-layer, and so on and so forth.Each of the sub-layers within the MQW layer is oppositely doped from itsadjacent sub-layer. That is, the various sub-layers within the MQW layerare doped in an alternating p-n fashion. The light emission efficiencydepends on the number of layers of alternating layers and thicknesses.

The doped layers and the MQW layer may all be formed by an epitaxialgrowth process known in the art. After the completion of the epitaxialgrowth process, an LED is created by the disposition of the MQW layerbetween the doped layers. When an electrical voltage (or electricalcharge) is applied to the doped layers of the LED devices 80, the MQWlayer emits radiation such as light. The color of the light emitted bythe MQW layer corresponds to the wavelength of the radiation. Theradiation may be visible, such as blue light, or invisible, such asultraviolet (UV) light. The wavelength of the light (and hence the colorof the light) may be tuned by varying the composition and structure ofthe materials that make up the MQW layer.

The LED devices 80 are coupled to die-bonding components 90. Thedie-bonding components 90 include a conductive material such as metal.In an embodiment, the die-bonding components 90 include gold and nickellayers. In other embodiments, the die-bonding components 90 may includelead-free solder such as a suitable alloy of tin (Sn), copper (Cu), andsilver (Ag).

As FIG. 2 illustrates, the LED devices 80 have a lateral dimension 100that is no greater than the lateral dimension 60 of the bonding pads 40.In an embodiment, the lateral dimension 100 is in a range from about 300microns to about 5000 microns. The LED devices 80 and the die-bondingcomponents 90 collectively have a thickness 110. In an embodiment, thethickness 110 is in a range from about 110 microns to about 400 microns.

The LED devices 80 are placed on the bonding pads through thedie-bonding components 90. For example, an auto die-to-waferpick-and-place machine may be used to accurately place the LED devices80 (and the die-bonding components attached thereto) on the bonding pads40. The flux material (shown as element 70 in FIG. 1) couples togetherthe bonding pads 40 and the die-bonding pads 90, respectively. However,the strength of coupling based on the stickiness of the flux material isnot very strong. Consequently, the LED devices 80 may experience lateraldisplacement or shift with respect to the bonding pads 40. When suchlateral displacement occurs in a later bonding process (for example abonding process that takes place in a reflow oven), the position-shiftedLED devices 80 is permanently bonded to the bonding pads 40 with theshift in place. This phenomenon is referred to as die-shift. Forexisting LED processes, such die-shift may exceed over 30 microns. Theseverity of die-shift under existing LED fabrication methodologies mayhandicap the applicability of advanced LED packaging/die processes. Inother words, advanced LED packaging/die processes have very lowtolerances for die-shift, which is less than some of the existing LEDprocesses.

According to various aspects of the present disclosure, a mold fixtureis used to substantially alleviate the die-shift issue discussed above.Referring to FIG. 3, a simplified top view of an embodiment of a moldfixture 150 is illustrated. The mold fixture 150 may be made of a metal,a quartz material, a sapphire material, or a ceramic material. The moldfixture 150 has a plurality of concave openings or recesses 170. In anembodiment, the number of recesses 170 corresponds to the number of LEDdevices placed on the sub-mount 30. The recesses 170 each have a lateraldimension 180, which may be measured in an X-direction or in aY-direction. The lateral dimension 180 of the recesses 170 is just alittle greater than the lateral dimension 100 of the LED devices 80(shown in FIG. 2). In an embodiment, the lateral dimension 180 is in arange from about 0.38 millimeters to about 5.1 millimeters.

The recesses 170 are to be used to cover the LED devices (e.g., LEDdevices 80) placed on the sub-mount 30. The recesses 170 are designed tohouse the LED devices therein during the reflow process or eutecticmetal bonding process and to have lateral dimensions small enough so asto restrict lateral displacement of the LED devices. In this manner, thedie-shifting issue discussed above will be substantially alleviated.This aspect of operation is discussed in more detail below.

The mold fixture 150 may also include one or more alignment marks 190and 191. In the illustrated embodiment, the alignment marks 190 and 191are located on opposite sides of the mold fixture 150, but it isunderstood that the alignment marks may be located in different areas ofthe mold fixture 150 in alternative embodiments. The alignment marks 190and 191 help align the mold fixture accurately with the sub-mount, sothat each recess 170 is aligned with a respective one of the LEDdevices.

FIG. 4 illustrates a simplified top view of a sub-mount 30 having aplurality of bonding pads 40 and a plurality of LED devices 80 that areplaced on the bonding pads 40, as well as a simplified top view of themold fixture 150. The sub-mount 30 also includes alignment marks 200 and201. In the illustrated embodiment, the alignment marks 200-201 aredisposed on opposite sides of the sub-mount 30.

The mold fixture 150 is positioned in a manner so that the alignmentmarks 190-191 are respectively aligned with the alignment marks 200-201of the sub-mount 30. Although the sub-mount 30 and the mold fixture 150are shown separately, it is understood that FIG. 4 is intended toportray a state of superposition between the sub-mount 30 and thefixture 150. That is, when the alignment marks 190-191 are respectivelyaligned with the alignment marks 200-201 of the sub-mount 30, the moldfixture 150 may be substantially disposed over and aligned with thesub-mount 30. In particular, the mold fixture 150 is designed andmanufactured with high precision instruments such that the dimensionsand locations of the recesses 170 and alignment marks 190 and 191 arefinely tuned and controlled. Here, once alignment is achieved betweenthe sub-mount 30 (below) and the mold fixture 150 (above), each of therecesses 170 is substantially aligned with a respective one of the LEDdevices 80 below. In some embodiments, an optical (e.g., laser)positioning system may also be employed to enhance the alignmentaccuracy. In other embodiments, the alignment marks are physical. Forexample, the alignment mark 190 may be a shape that fits in a slot.Although the drawings show a cross shape, the alignment marks 190/191and 200/201 may be any other appropriate shape.

Once alignment is achieved between the sub-mount 30 and the mold fixture150, the mold fixture 150 is placed on the sub-mount 30, with eachrecess 170 covering a respective one of the LED devices 80 therebelow.This is illustrated in FIG. 5, which shows a simplified fragmentarycross-sectional view of the sub-mount 30 and an embodiment of the moldfixture 150A after the mold fixture 150A is placed on top of thesub-mount 30. The LED devices 80 are covered by recesses 170A. In theembodiment illustrated herein, the recesses 170A have approximatelytrapezoidal shapes with sloped or tapered sidewalls (i.e., the recessesare wider toward the surface of the mold fixture). The sloped sidewallsof the recesses 170A make it easier for the LED devices 80 to be“inserted” into the recesses as the mold fixture 150A is being placed onthe sub-mount 30. It is understood, however, that the recesses 170A mayhave other suitable shapes in alternative embodiments, some of whichwill be shown in the following figures and discussed in more detailbelow.

The LED devices 80 are in effect “pinned” by the recesses 170A, suchthat the lateral movement of the LED devices 80 is limited orrestricted. In other words, it is difficult for the LED devices 80 tomove in any lateral direction because the sidewalls of the recesseswould block or prevent such movement. In this manner, the LED devices 80can be held in place during later fabrication stages, such as during athermal reflow process. Consequently, the undesirable die-shift issuesdiscussed above can be substantially alleviated. In an embodiment, theamount of die-shift in any lateral direction is less than about 10microns, for example within about 5 microns.

Though not specifically shown for the sake of simplicity, it isunderstood that the mold fixture 150A can be secured with respect to thesub-mount 30. For example, a screw, a chuck, a stand, or anothersuitable mechanism may be used to attach the mold fixture 150A to thesub-mount 30. The securing mechanism allows the mold fixture 150A toremain stationary relative to the sub-mount 30 (and thus to the bondingpads 40) even as other forces may be applied to the mold fixture 150A,forces that would have otherwise shifted the mold fixture 150A. Suchshift of the mold fixture 150A with respect to the sub-mount 30 wouldhave been undesirable, since it would have led to the shifting of theLED devices 80 as well. Therefore, the mold fixture 150A is implementedto be securely attached to the sub-mount 30 so that substantially littleor no shifting between the mold fixture 150A and the sub-mount canoccur.

In the illustrated embodiment, the upper surface of the LED devices 80comes into physical contact with the LED devices 80. As such, a force250 can be applied to the LED devices 80 through the mold fixture 150A.For example, the force 250 may be the weight of the mold fixture 150A inan embodiment. The weight of the mold fixture 150A can be adjusted bychanging the size (e.g., the thickness of the mold fixture 150A),material composition, and/or shape of the mold fixture 150A during thedesign and fabrication of the mold fixture 150A. Thus, a desired amountof force 250 can be obtained by adjusting the weight of the mold fixture150A. In other embodiments, the force 250 may be applied externally. Forexample, a weight may be placed on the upper surface of the mold fixture150A, or a machine may push down on the upper surface of the moldfixture 150A, where the machine can deliver an adjustable amount offorce. In any case, it can be seen that the force 250 is tunable oradjustable. The force 250 is at least partially delivered to the LEDdevices 80, which is beneficial because the application of the force 250may aid the bonding between the LED devices 80 and the bonding pads 40in a bonding process.

FIG. 6 illustrates a simplified fragmentary cross-sectional view ofanother embodiment of a mold fixture 150B after it is placed on thesub-mount 30. For the sake of consistency and clarity, similarcomponents in FIGS. 5 and 6 are labeled the same. Compared to the moldfixture 150A shown in FIG. 5, the recesses 170B of the mold fixture 150Bhave different depths and lateral dimensions. For example, the recesses170B of the mold fixture 150B may be shallower but wider than those ofthe mold fixture 150A, as is illustrated in FIG. 6. Alternatively, therecesses 170B of the mold fixture 150B may be deeper and/or narrowerthan those of the mold fixture 150A, depending on the fabrication needsand requirements. The sizes and shapes of the recesses 170B may beadjusted to account for the degree of alignment and/or restriction ondie-shift. In addition, the recesses 170B may have substantiallystraight (vertical) profiles rather than tapered profiles in someembodiments. It is understood that similar to the mold fixture 150A, themold fixture 150B may also be secured to the sub-mount 30, and a forcemay also be applied through the mold fixture 150B to facilitate thebonding between the LED devices 80 and the bonding pads 40.

FIG. 7 illustrates a simplified fragmentary cross-sectional view of yetanother embodiment of a mold fixture 150C after it is placed on thesub-mount 30. For the sake of consistency and clarity, similarcomponents in FIGS. 5-7 are labeled the same. The recesses 170C of themold fixture 150C may have tapered profiles in some embodiments orsubstantially straight profiles in other embodiments. The recesses 170Cof the mold fixture 150C may also completely cover the bonding pads 40.Stated differently, the bottom surface of the mold fixture 150C may comeinto physical contact with the upper surface of the sub-mount 30. It isalso understood that similar to the mold fixture 150A, the mold fixture150C may be secured to the sub-mount 30, and a force may also be appliedthrough the mold fixture 150C to facilitate the bonding between the LEDdevices 80 and the bonding pads 40.

Additional configurations of the mold fixture 150 are not discussedherein for the sake of simplicity, but is understood that the sizes andshapes of the recesses 170 may be adjusted to account for differentconsiderations such as alignment and restriction on the amount ofdie-shift.

Referring to FIG. 8, a bonding process 300 is performed to bond the LEDdevices 8-to the bonding pads 40. The mold fixture 150 remains placed onthe sub-mount 30 while the bonding process 300 is being performed. Assuch, the amount of die-shift during the bonding process 300 issubstantially reduced. Note that the edge of the mold fixture 150 mayextend past the top of the bond pads 40. In an embodiment, the bondingprocess 300 includes a thermal process that is performed at a reflowoven 320. The thermal process may be performed at temperatures greaterthan about 210 degrees Celsius. The material composition of the moldfixture 150 is selected such that it can withstand the high temperaturesof the thermal process. After the bonding process is finished, the moldfixture 150 can be removed. It is also understood that other methods ofbonding may be used in alternative embodiments, such as eutecticbonding. Furthermore, additional processes may be performed to finishthe packaging of the LED devices, but they are not discussed herein forthe sake of simplicity.

FIG. 9 is a flowchart of a method 10 for fabricating a photonic deviceaccording to various aspects of the present disclosure. Referring toFIG. 9, the method 10 includes block 12, in which a substrate isprovided. The substrate has a plurality of conductive pads disposedthereon. The conductive pads may be bonding pads and may include a metalmaterial. The method 10 includes block 14, in which a plurality ofsemiconductor dies is placed on the plurality of conductive pads,respectively. The semiconductor dies may include photonic devices suchas LED devices. The method 10 includes block 16, in which a mold deviceon the substrate. The mold device has a plurality of recesses that coverthe semiconductor dies. The recesses each cover a respective one of thesemiconductor dies in a manner such that the recesses restrict thelateral movement of the semiconductor dies. The method 10 includes block18, in which the semiconductor dies are bonded to the conductive pads.The bonding process may include a thermal reflow process performed in areflow oven. It is understood that additional processes may be performedbefore, during, or after the blocks 12-18 discussed herein to completethe fabrication of the photonic devices.

The embodiments of the present disclosure discussed above offeradvantages over existing methods. However, that other embodiments mayoffer different advantages, and that no particular advantage is requiredfor any embodiment. One of the advantages is that the LED die-shift issubstantially reduced. Through the use of the mold fixture, the LEDdevices can be held in place when they are bonded to the bonding pads.As a result, the die-shift may be controlled to be within about 5microns, which allows advanced packaging processes to be applied later.

An additional advantage is that the application of the mold fixture doesnot involve extra fabrication stages or additional processing time. Themold fixture is fabricated in a manner to withstand high temperatures,and thus it requires no modifications to the bonding processes either.Therefore, LED production throughput is not reduced.

Yet a further advantage is that the mold fixture can be used to applypressure to the LED devices to facilitate the bonding process. Thepressure is tunable through adjusting the weight of the mold fixture ora force applied to the mold fixture by another machine. Other advantagesmay exist, but they are not discussed herein for the sake of simplicity.

One of the broader forms of the present disclosure involves a method.The method includes: providing a substrate having a plurality ofconductive pads; placing a plurality of semiconductor dies on theplurality of conductive pads; placing a mold device on the substrate,the mold device having a plurality of recesses, wherein the placing themold device is carried out in a manner such that each of thesemiconductor dies is covered by a respective one of the recesses; andthereafter bonding the semiconductor dies to the conductive pads.

In various embodiments, the placing the mold device is carried out in amanner such that each recess substantially restricts movement of thesemiconductor die that is covered by the recess.

In some embodiments, the placing the mold device is carried out in amanner such that each semiconductor die covered by the recess has amovement range that is less than about 5 microns in any lateraldirection.

In certain embodiments, the placing the mold device is carried out in amanner such that the mold device is secured with respect to thesubstrate, so that the mold device is substantially free of lateralmovement with respect to the substrate.

In some embodiments, the placing the mold device is carried out in amanner such that the mold device applies pressure to the semiconductordies.

In some embodiments, the recesses each have a sloped profile. In otherembodiments, the recesses have different profiles based on its positionrelative to a center of the sub-mount. In still other embodiments, therecesses each have vertical sidewalls.

In some embodiments, the bonding includes heating the substrate, thesemiconductor dies, and the mold device in a reflow oven.

In some embodiments, the method further includes: applying a fluxmaterial on each of the conductive pads before the semiconductor diesare placed on the conductive pads; and aligning each of the recesses ofthe mold device with a respective one of the semiconductor dies beforethe mold device is placed on the substrate.

In various embodiments, the semiconductor dies include light-emittingdiode (LED) devices.

Another of the broader forms of the present disclosure involves a methodof fabricating a photonic device. The method includes: providing a waferhaving a plurality of bonding pads disposed thereon; positioning aplurality of photonic devices on the plurality of bonding pads,respectively; covering the photonic devices with a mold fixture having aplurality of concave openings, wherein each photonic device is securedby a respective one of the concave openings in a manner such that alateral shift between each photonic device and the respective bondingpad therebelow is less than a predefined value; and bonding the photonicdevices to the bonding pads while the photonic devices are covered bythe mold fixture, wherein the bonding is carried out at least in partthrough a thermal process.

In some embodiments, the covering is carried out in a manner such thatthe predefined value is about 10 microns.

In some embodiments, the covering includes securing the mold fixturesuch that the mold fixture is substantially free of lateral shift withrespect to the wafer.

In some embodiments, the method further includes: applying a tunableamount of pressure through the mold fixture to each of the photonicdevices.

In some embodiments, the concave openings each have a taperedcross-sectional profile.

In some embodiments, the method further includes: before thepositioning, applying a flux material on each of the bonding pads in amanner so that the photonic devices are coupled to the bonding padsthrough the flux material; and before the covering, aligning the moldfixture with the wafer in a manner such that each concave opening issubstantially aligned with a respective one of the photonic devices.

Still another of the broader forms of the present disclosure involves amethod of light-emitting diode (LED) packaging. The method includes:providing a sub-mount having a plurality of bonding pads disposedthereon; coupling a plurality of LED dies to the plurality of bondingpads, wherein each LED die is coupled to a respective one of the bondingpads; providing a mold apparatus, the mold apparatus including aplurality of concave recesses; placing the mold apparatus over thesub-mount, wherein each LED die is housed in a respective one of therecesses; and thereafter heating the sub-mount, the LED dies, and themold apparatus in a thermal reflow process, thereby causing the LED diesto be bonded to the bonding pads, respectively; wherein each recesssubstantially restricts a positional shift of the LED die below withrespect to the bonding pad coupled thereto during the heating.

In some embodiments, the placing the mold apparatus is carried out in amanner such that the mold apparatus is position-secured relative to thesub-mount.

In some embodiments, the placing the mold apparatus includes applying apredetermined amount of pressure to the LED dies through the moldapparatus.

In some embodiments, the placing the mold apparatus includes aligningthe recesses with the LED dies through an optical positioning process.

In some embodiments, the recesses of the mold apparatus each have anon-uniform cross-sectional profile.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method, comprising: providing a substratehaving a plurality of conductive pads; placing a plurality ofsemiconductor dies on the plurality of conductive pads in a manner suchthat an entire bottom surface of each of the semiconductor dies isplaced on a respective conductive pad; placing a mold device on thesubstrate, the mold device having a plurality of recesses, wherein theplacing the mold device includes covering each of the semiconductor diesby a respective one of the recesses; and thereafter bonding thesemiconductor dies to the conductive pads.
 2. The method of claim 1,wherein the placing the mold device substantially restricts movement ofthe semiconductor dies that are covered by recesses in the mold device.3. The method of claim 2, wherein the placing the mold device includesrestricting a movement range of each semiconductor die covered by therecess to be less than about 5 microns in any lateral direction.
 4. Themethod of claim 1, wherein the placing the mold device includes securingthe mold device with respect to the substrate, so that the mold deviceis substantially free of lateral movement with respect to the substrate.5. The method of claim 1, wherein the placing the mold device includesapplying pressure to the semiconductor dies through the mold device. 6.The method of claim 1, wherein the recesses each have a sloped profile.7. The method of claim 1, wherein the bonding includes heating thesubstrate, the semiconductor dies, and the mold device in a reflow oven.8. The method of claim 1, further including: applying a flux material oneach of the conductive pads before the semiconductor dies are placed onthe conductive pads; and aligning each of the recesses of the molddevice with a respective one of the semiconductor dies before the molddevice is placed on the substrate.
 9. The method of claim 1, wherein thesemiconductor dies include light-emitting diode (LED) devices.
 10. Amethod of light-emitting diode (LED) packaging, comprising: providing asub-mount having a plurality of bonding pads disposed thereon; couplinga plurality of LED dies to the plurality of bonding pads, wherein eachLED die is coupled to a respective one of the bonding pads throughdirect surface contact; providing a mold apparatus, the mold apparatusincluding a plurality of concave recesses; placing the mold apparatusover the sub-mount, wherein each LED die is housed in a respective oneof the recesses; and thereafter heating the sub-mount, the LED dies, andthe mold apparatus in a thermal reflow process, thereby causing the LEDdies to be bonded to the bonding pads, respectively; wherein each recesssubstantially restricts a positional shift of the LED die below withrespect to the bonding pad coupled thereto during the heating.
 11. Themethod of claim 10, wherein the placing the mold apparatus includespositionally securing the mold apparatus relative to the sub-mount. 12.The method of claim 10, wherein the placing the mold apparatus includesapplying a predetermined amount of pressure to the LED dies through themold apparatus.
 13. The method of claim 10, wherein the placing the moldapparatus includes aligning the recesses with the LED dies through anoptical positioning process.
 14. The method of claim 10, wherein therecesses of the mold apparatus each have a non-uniform cross-sectionalprofile.
 15. A method of light-emitting diode (LED) packaging,comprising: providing a sub-mount having a plurality of conductiveelements disposed thereon; providing a mold having a plurality ofconcave recesses; placing a plurality of LED dies to the plurality ofconductive elements, wherein each LED die is placed to a different oneof the conductive elements, and wherein a lateral dimension of each LEDdie is smaller than a lateral dimension of the conductive element towhich the LED die is coupled; thereafter covering the plurality of LEDdies with the mold over the sub-mount, wherein the plurality of LED diesis aligned with the plurality of recesses, respectively, such that eachrecess restricts movements of the LED die underneath; and performing aheating process to the sub-mount, the LED dies, and the mold, therebycausing the plurality of LED dies to be bonded to the plurality ofconductive elements, respectively.
 16. The method of claim 15, furthercomprising: securing the mold to the sub-mount before the performing theheating process, such that the mold is free of lateral movement relativeto the sub-mount.
 17. The method of claim 15, further comprising:applying a downward force to the mold after the covering the pluralityof LED dies.
 18. The method of claim 15, wherein the covering theplurality of LED dies is performed at least in part through an opticalpositioning process.
 19. The method of claim 15, wherein the recesses ofthe mold each have a non-uniform cross-sectional profile.
 20. The methodof claim 19, wherein at least some of the recesses each have atrapezoidal cross-sectional profile.